This invention relates to a process for selectively hydroformylating an acrolein acetal on an unsaturated carbon atom other than the terminal carbon atom. More particularly, this is a one-step process for effecting such hydroformylation using as a catalyst an amine-resin supported rhodium-cobalt carbonyl bimetallic cluster.
U.S. Pat. Nos. 4,144,191 and 4,197,414 disclose the use of rhodium-cobalt carbonyl bimetallic clusters supported by amine resins as catalysts for the hydroformylation of olefins. These patents teach that any olefin that can be converted to an aldehyde by known oxo processes can be converted to alcohols by the process described therein. The distribution of isomers in the hydroformylated product is not disclosed, but the distribution of alcohol isomers would be expected to be similar to the aldehyde distribution obtained with the prior art oxo process.
U.S. Pat. No. 4,017,550 teaches that cyclic acetals of acrolein can be hydroformylated in the presence of phosphine-modified cobalt carbonyl complexes of rhodium carbonyl complexes. The hydroformylation occurs predominantly on the terminal unsaturated carbon atom of the acrolein acetal.
Nothing in the prior art discloses how to selectively hydroformylate an acrolein acetal on an unsaturated carbon atom other than the terminal carbon atom. Internal hydroformylation of an acrolein acetal is desirable because the hydroformylated product can be readily hydrolyzed to 2-methyl-1,3-propanediol. In turn, the 2-methyl-1,3-propanediol can be dehydrated by methods known to the art to produce 2-methyl-1-propen-3-ol. The 2-methyl-1-propen-3-ol is of interest because it can be oxidized by standard techniques to produce methacrylic acid or its corresponding esters. It follows that selective internal hydroformylation of acrolein acetals would be desirable because it affords a convenient starting material for the preparation of methacrylic acid.